Reaction Kinetics, Mechanisms and Catalysis最新文献

Pd/γ- Al₂O₃ catalyst for hydrogen oxidation at room temperature was prepared by impregnation of Pd(OH)₂ sol. The prepared catalyst was tested by hydrogen oxidation at room temperature in a closed-loop differential reactor and compared with the catalyst prepared by impregnation of PdCl₂ aqueous solution. The catalysts were characterized by CO chemisorption, UV–vis, and XRD spectroscopy. The presence of Pd(OH)₂ sol in the impregnation solution was confirmed by dynamic light scattering, UV–vis spectroscopy and potential measurements versus pH by electrophoresis. The penetration depth of Pd in the catalyst was measured by a stereomicroscope coupled with a computer and a CCD camera. Compared with the catalyst prepared by impregnation of Pd(OH)₂ sol with the catalyst prepared by impregnation of PdCl₂ aqueous solution, the catalyst was much more active for the same Pd content, because of the high Pd dispersion and the low penetration depth in the catalyst. Pd(OH)₂ sol impregnation can reduce palladium consumption by 40% compared to PdCl₂ aqueous impregnation.

The transfer hydrogenation (TH) of butyl sorbate was investigated with the aim of determining optimal reaction conditions regarding conversion and selectivity towards desired hydrogenated products. Despite TH being widely used for carbonyls and simple olefins, its selective application to conjugated dienes remains virtually untested; nevertheless, the TH products of butyl sorbate are of significant industrial relevance as flavor and fragrance ingredients. A systematic study was therefore performed to evaluate the effect of catalyst type and loading, ligand concentration, solvent, temperature, hydrogen donor, and the ratio of formic acid to triethylamine. The most effective system in terms of conversion employed 0.1 mmol palladium acetate as the catalyst, 0.1 mmol 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos) as the ligand, and 4 mmol formic acid/triethylamine mixture (5:2) as the hydrogen donor in tetrahydrofuran at 90 °C. Under these conditions, complete conversion of butyl sorbate was achieved within the first hour of the reaction. However, when selectivity was considered, the most favorable conditions were obtained with 0.1 mmol palladium acetate, 0.1 mmol Xantphos, and a 4 mmol ammonium formate as the hydrogen donor in tetrahydrofuran at 90 °C, affording 87% conversion after 3 h and an excellent 88% selectivity towards butyl (E)-2-hexenoate.

The degradation of phenol was carried out using Bi-Zn layered double hydroxides catalyst intercalated with copper oxide. Catalyst was prepared by simple co-precipitation reaction. The catalyst was characterized by XRD, SEM and FTIR techniques. XRD patterns of these precursors seemed crystalline, similarly to the literature reported for brucite like LDHs materials. Calcined LDH material was an efficient catalyst to oxidize phenol up to 88% at pH 6 when initial concentration was 50 mg L⁻¹, agitation time was 300 min and catalyst dosage was 400 mg. HPLC results confirmed the phenol is converted into catechol by producing HO* free radical (in the presence of H₂O₂) by LDH.The efficiency of catalyst was examined by performing different experiments at same conditions with only H₂O₂ and partial oxidation of phenol was recorded.

In this study, cerium oxide-based nanocomposites integrated with graphite, CeO₂@ graphite, Ce_0.50Al_0.50O_2-δ@graphite, Ce_0.90Cu_0.10O_2-δ @ graphite, and Ce_0.60Zn_0.40O_2-δ@graphite were synthesized via a simple in-situ chemical method. Their structural, chemical, and morphological features were characterized using XRD, FTIR, EDAX, and SEM. The XRD pattern of graphite shows a prominent (002) reflection at 2θ ≈ 26.3–26.6°, confirming its characteristic layered structure. The ceria–graphite composites retain this graphite peak and also exhibit CeO₂ reflections. The FTIR spectra show a graphite-related peak, while the composites exhibit a 1632 cm⁻¹ hydroxyl band and a 400–600 cm⁻¹ metal–oxygen vibration region. From the EDAX spectra, peaks corresponding to Ce, Al, Cu, Zn, O, and C were clearly observed. The SEM images show flake-like graphite filaments with a rough surface decorated by nanosized doped-ceria grains (200–500 nm). The photocatalytic activity of the nanocomposites was assessed using Rhodamine B under UV light, and the Ce_0.50Al_0.50O_2-δ@graphite sample showed the highest degradation efficiency of 82.21%. Graphite incorporation enhanced performance by improving charge separation and surface interaction. The effects of pH and initial dye concentration were also examined. Overall, the Al-doped ceria–graphite composite demonstrates strong potential for environmental remediation applications.

The article presents a study on the valorization of Spent Bleaching Earth (SBE), a by-product produced in large quantities by edible oil refineries, particularly in Algeria, where it poses environmental problems due to its high content of residual oils and contaminants. The main objective is to optimize the regeneration of this earth by thermal treatment in order to transform it into an effective adsorbent, particularly for the removal of methylene blue, a model dye. The study is carried out in two stages: first, the effect of carbonization temperature (400 to 900 °C) on the structural and textural properties of SBE is examined, revealing that a temperature of 800 °C maximizes microporosity before the structure collapses at 900 °C. Then, an optimization of the time and temperature parameters is carried out via a Face-Centered Central Composite Design (FCCCD) and a response surface methodology, which makes it possible to identify optimal conditions around 600 °C and 48 min to obtain a material whose adsorption capacity reaches 72.8%, experimentally validated at 71.04%. The analyses (ATG, FTIR, DRX, BET) confirm that the thermal treatment eliminates organic compounds and develops microporosity without altering the silicate structure up to 800 °C, and that temperature is the most determining factor for the performance of the regenerated material. This work thus demonstrates that SBE can be effectively valorized by optimized thermal regeneration, offering a sustainable solution for the management of this hazardous waste while producing a high-performance adsorbent for water treatment.

This study theoretically investigated the selectivity and reactivity in the 32CA reaction of C,N-diarylnitrone (X1) with arylallene (X2) and N-aryl-C-carbamoyl nitrone (B1) with methyl buta-2,3-dienoate (B2), leading to methylideneisoxazolidine. We employed density functional theory (DFT) at the ωB97XD/6-311+G(d,p). The 32CA reaction of X1 to X2 is a one-step mechanism, with path A being the most kinetically favored, leading to the formation of 5-methylideneisoxazolidine diastereoisomeric pairs (P3A + P4A). Substitutions of –CN and -OCH₃ on X2 influence the regioselectivity of the cycloaddition process. CN substitution gives the 5-methylideneisoxazolidine cycloadduct, while OCH₃ substitution gives the 4-methylideneisoxazolidine. The reaction of B1 with B2 occurs at the internal C=C olefinic bond to regioselectively yield the 5-methylideneisoxazolidine adduct. Theoretical computations suggest that the phenyl group on X2 behaves as an electron-withdrawing group. The GEDT values for the 32CA of X1 to X2 exhibit a nonpolar character, classified as REDF, while those involving B1 to B2 display a slightly polar character, classified as FEDF.

To address the issue of high electron–hole recombination rate in conventional catalysts used for the photocatalytic treatment of ballast water, this work designed and synthesized a Bi₂Sn₂O₇/BiOCl heterojunction photocatalyst via a simple hydrothermal method. After 30 min of simulated sunlight irradiation, it exhibited outstanding inactivation efficiency against marine bacteria. The Bi₂Sn₂O₇/BiOCl-0.6 heterojunction achieved an inactivation efficiency of up to 92%, 2.4 times higher than that of pure Bi₂Sn₂O₇. Performance experiments and electrochemical analysis demonstrate that the heterojunction optimizes electron transfer pathways, enhances electron–hole separation efficiency, and promotes the generation of hydroxyl radicals, thereby significantly improving photocatalytic performance. This study offers novel insights for developing highly efficient photocatalytic ballast water treatment materials suitable for complex marine environments.

Graphical abstract

Arene Ru(II) complexes; (η⁶-Benzene)chloro-bis(triphenylphosphino)ruthenium(II) chloride, C1, (η⁵-cyclopentadienyl)chloro-bis(triphenylphosphino)ruthenium(II) Chloride, C2, (η⁶-Benzene)chloro{bis(diphenylphosphino)methane}ruthenium(II) Chloride, C3, η⁵-cyclopentadienyl)[bis(diphenylphosphino)methane]ruthenium(II), C4 (η⁶-Benzene)chloro{1,2-bis(diphenylphosphino)ethane}ruthenium(II) Chloride, C5 and (η⁶-Benzene)chloro{1,3-bis(diphenylphosphino)propane}ruthenium(II) Chloride, C6 were successfully synthesized by modified literature methods. The rates of chloro substitution and mechanism of reactions of the arene Ru(II) complexes by thiourea nucleophiles were studied under pseudo first order conditions in 0.1 M NaClO₄/LiCl methanol solution as a function of nucleophile concentration and temperature. The reactions were monitored using the UV–vis absorption spectrophotometer or stopped flow spectrophotometer for fast reactions. The coordinated arene ligand donates electrons towards the Ru metal ion centre and its π -electron cloud presents an electrostatic repulsive effect onto and around the Ru centre as measured by the projected cone angle. The bidentate bis(diphenylphosphino)methane ligand hinders the approach of nucleophiles during the substitution process. When the bis(diphenylphosphino)methane chelate is expanded through the introduction of a methylene carbon within the bridge, the steric hindrance to the approach of nucleophiles is reduced because of the trough like conformation of the alkyl chain which traps the nucleophiles within the coordination sphere. This enhances the reactivity by a factor of 10³. The observed reactivity trends are supported by DFT calculations. The entropy of activation values are positive indicating that the mechanism of substitution has interchange dissociative (I_D) character.

A novel anhydrous sol–gel synthesis of carbon-modified silicon dioxide nanoparticles (SiO-NPs) is reported, utilizing oxalic acid as both a catalyst and a structuring agent. This unique approach facilitates the formation of a silicon oxalate intermediate network via transesterification, which upon thermal decomposition yields a defect-rich SiO₂ matrix with integrated carbon species (Si–O–C and residual Si–C bonds). Comprehensive characterization by FTIR, XPS, UPS, UV–Vis, and PL confirmed the amorphous nature, sub-stoichiometric Si/O ratio, and the presence of hybridized SiOC states and various intrinsic defect centers, which collectively modify the material's electronic and optical properties, including a reduced band gap and broad photoluminescence. The functional performance was demonstrated in a highly efficient two-stage process for methylene blue removal, achieving 73.95% overall efficiency through initial dark adsorption followed by rapid photo-induced degradation. The photoactivity is attributed to light absorption by carbon-induced defect states, leading to reactive oxygen species generation. This work presents a cost-effective route to synthesize dual-functional nanomaterials, highlighting their potential for advanced water treatment and contributing to the understanding of defect engineering in wide-bandgap oxides.

The objective of this study was to evaluate the effect of grape polysaccharide content on the biodegradable polymeric films derived from cornmeal flour starch properties. The physicochemical and thermal characteristics of starch films containing 5%, 10%, and 15% grape-derived polysaccharides were investigated. The experiments showed that the addition of 5% polysaccharides improved water solubility by 14.18% compared to the control film, whereas increasing the polysaccharide content to 10% and 15% resulted in decreases of 2.11% and 4.07%. Nevertheless, high polysaccharide concentration resulted in increased swelling index and thermal stability. The maximum decomposition temperature rose from 319.50 °C for samples with 5% polysaccharides to 328.33 °C for those with 15% polysaccharides, while the swelling index increased from 70.08% in the control sample to 122.04% in the sample with 10% polysaccharides. To identify the decomposition mechanism for each degradation stage, the Coats-Redfren analysis was carried out. The data suggests that the thermal decomposition of films with polysaccharides involves three-dimensional diffusion for first degradation step, indicating low volatile compounds in the samples’ structure. The second degradation stage corresponds to the first order reaction, probably due to internal carbon rearrangement in the chemical structure. To calculate the apparent activation energies, model-free and nonlinear estimation methods were employed.